Curable resins and articles made therefrom

ABSTRACT

Optical devices of excellent optical and physical properties produced from cured resins are disclosed. The resins and/or the cured hybrid polymer material made with the resins are characterized by a high level of cycloaliphatic-containing groups. Specific additives that can participate in crosslinking the curable polysiloxane provide additional physical property advantages.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/813,686, filed Jun. 11, 2010, which claims the benefit ofthe filing date of U.S. Provisional Patent Application No. 61/268,488filed Jun. 12, 2009, the disclosures of which are hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION

Known materials are often incapable of satisfactorily balancing the manyrequirements necessary for use as optical devices. Indeed, the oftencompeting criteria for successful optical polymers are numerous andinclude: (1) material must have a high transparency with little or noyellowing (greater than 90% transmission between 400 nanometers and 700nanometers); (2) low cure shrinkage (less than 4% and in otherembodiments, less than 2% linear shrinkage); (3) low “reflow” shrinkagealso known as low post thermal shrinkage (less than 2% linear shrinkageupon temperature excursion between room temperature and up to 280° C.,in another embodiment, less than 1% linear shrinkage under theseconditions); (4) high fracture toughness (not brittle or crumbly >1.0MPa); (5) high refractive index (greater than 1.47, and in anotherembodiment, greater than 1.49); (6) low dispersion (a relatively high“Abbe” number V_(d)—greater than 45 and in another embodiment greaterthan 53); (7) ease of release from a mold; (8) good adhesion tosubstrates (typically quartz, glass or SiO₂, which can be furtheroptimized with additives); (9) low coefficient of thermal expansion (CTEof 120 ppm/° C., and in another embodiment less than 80 ppm/° C.); (10)a low change of refractive index with temperature (dn/dT of less than100×10⁻⁶ RIU/° C.); and (11) must pass thermal shock (100 cycles of −40°C. to 85° C. over 2.5 minutes (i.e., 50° C./min)) without cracking ordelamination and with less than 1% shrinkage. Perhaps the most difficultof these to meet are the requirements of low cure shrinkage, lowdispersion, high refractive index, and high fracture toughness.

Epoxycyclohexyl-siloxane hybrid resins have been previously proposed byCrivello and others (see for example Crivello et al. Chemistry ofMaterials (2001) vol. 13, p. 1932). Their main advantage is their lowcure shrinkage, and high transparency. While some resins based on 100%(epoxycyclohexyl)ethyltrimethoxysilane (ECHETMS) manufactured byPolyset, have Abbe number values or V_(d) near 56 or higher andrefractive indexes of 1.5 or higher, the cured ECHETMS resin exhibitpractically no glass transition and low fracture toughness(brittleness). This leads to cracking and breaking when films or otherfabricated parts (optical devices) supported on glass substrates undergothermal annealing (to between room temperature and 130° C.), reflow, orthermal shock. Overcoming low fracture toughness of cationicepoxycyclohexyl-based resins in general, and ECHETMS-based resins inparticular, is a challenging issue that has received considerableattention in the published literature.

See Wu, et al., “Siloxane modified cycloaliphatic epoxide UV coatings,”36 Progress in Organic Coatings (1999) 89-101, which teachesmodification of cycloaliphatic epoxide/caprolactone polyol coatings withsiloxane polyols. See Dworak & Soucek, “Synthesis of cycloaliphaticsubstituted silane monomers and polysiloxanes for photocuring,” 37Macromolecules (2004) 9402-17, which describes photocurable materialsincluding cycloaliphatic epoxide terminatedpoly(dimethylsiloxane-CO-methylhydrosiloxane and hydridefunctionalilzedpoly(dicycloaliphatic siloxane-CO-cycloaliphatic hydroxiloxane). Seealso Soucke et al., “A new class of silicone resins for coatings,” 4 J.Coat Techn. Res. Vol. 3 (2007) 263-74.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the invention provides a photocurable and/or thermallycurable resin (“PT curable resin”) of excellent optical propertiescapable of being used for producing optical devices or coatings foroptical devices having a high refractive index of greater than 1.48 andoptical dispersion, as measured by Abbe number, of greater than 45. Inanother aspect of the invention, there is provided a PT curable resinhaving excellent optical properties capable of being used for producingoptical devices or coatings for optical devices having a high refractiveindex of greater than 1.49 and an Abbe number of greater than 53.Optical devices produced from these PT curable resins or coatings foroptical devices comprising these PT curable resins are alsocontemplated.

Another aspect of the invention is a method of providing fracturetoughness and durability to a PT curable resin of excellent opticalproperties without unduly compromising those optical propertiescomprising curing a PT curable resin with an effective amount of atleast two additives selected from the group consisting ofhydroxyoxetanes, diglycidyl ethers, alcohols and divinyl ethers, and inone particular embodiment, hydroxyoxetane and a glycidyl ether are usedto produce a crosslinked solid hybrid polymer material. Optical devicesand coatings for optical devices made using this method are alsocontemplated.

In still another aspect of the invention, there is provided acrosslinked solid hybrid polymer material produced from a mixture of PTcurable resin, at least two additives selected from the group consistingof hydroxyoxetanes, diglycidyl ethers, alcohols and divinyl ethers, andin one particular embodiment, hydroxyoxetane and a glycidyl ether. Theresulting solid hybrid polymer material has excellent opticalproperties, rendering it useful and capable of being used for producingoptical devices or coatings for optical devices having a high refractiveindex of greater than 1.48, an Abbe number of greater than 45, a lowcure shrinkage of less than 3%, and high fracture toughness. Opticaldevices produced from this material and coatings produced for use onoptical devices made from this material are also contemplated.

In yet another aspect of the invention, there is provided a cured solidhybrid polymer of excellent optical properties having a refractive indexgreater than 1.49, an Abbe number greater than 53, low cure shrinkage(less than 2% linear shrinkage), and high fracture toughness.

At least some of the PT curable resins described herein can be reactedwith up to about 40% of a mixture of at least two of a hydroxyoxetane, aglycidyl ether, a divinyl ether and/or an alcohol to form a cured solidhybrid polymer having a refractive index of 1.48 or more, an Abbe numberof 45 or more, and sufficient fracture toughness. Optical devices andcoatings for optical devices made from these materials are alsocontemplated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph summarizing the optical properties of various resins.

DETAILED DESCRIPTION

While the specification concludes with the claims particularly pointingand distinctly claiming the invention, it is believed that the presentinvention will be better understood from the following description. Allpercentages and ratios used herein are by weight of the totalcomposition and all measurements made are at 25° C. and normal pressureunless otherwise designated. All temperatures are in Degrees Celsiusunless specified otherwise. The present invention can comprise (openended) or consist essentially of the components of the present inventionas well as other ingredients or elements described herein. As usedherein, “comprising” means the elements recited, or their equivalent instructure or function, plus any other element or elements which are notrecited. The terms “having” and “including” are also to be construed asopen ended unless the context suggests otherwise. As used herein,“consisting essentially of” means that the invention may includeingredients in addition to those recited in the claim, but only if theadditional ingredients do not materially alter the basic and novelcharacteristics of the claimed invention. Preferably, such additiveswill not be present at all or only in trace amounts. However, it may bepossible to include up to about 10% by weight of materials that couldmaterially alter the basic and novel characteristics of the invention aslong as the utility of the compounds (as opposed to the degree ofutility) is maintained. All ranges recited herein include the endpoints,including those that recite a range “between” two values. Terms such as“about,” “generally,” “substantially,” and the like are to be construedas modifying a term or value such that it is not an absolute, but doesnot read on the prior art. Such terms will be defined by thecircumstances and the terms that they modify as those terms areunderstood by those of skill in the art. This includes, at very least,the degree of expected experimental error, technique error andinstrument error for a given technique used to measure a value.

Note that while the specification and claims may refer to a finalproduct such as, for example, a poly(meth)acrylate or polysiloxanecontaining a particular monomer or a particular distribution ofmonomers, it may be difficult to tell from the final product that therecitation is satisfied. However, such a recitation may be satisfied ifthe materials used prior to final production meet that recitation.Indeed, as to the identity of any component or the presence of anyproperty or characteristic of a final product which cannot beascertained directly, it is sufficient if that component or propertyresides in an earlier production step.

“Optical devices” as used herein include lenses, waveguides, anddiffractive optical components. Optical devices may be produced usingany conventional process.

It has been surprisingly discovered that the use of cycloaliphaticgroups in the resins of the invention leads to an increase in both therefractive index and the Abbe number. This trend is opposite to thatwhich is seen with most materials, in which an increase in refractiveindex is generally accompanied by a decrease in the Abbe number (i.e.,an increase in optical dispersion).

Without wishing to be bound by any theory of operation, it is believedthat that this unexpected trend is associated with the fact that cycliccompounds absorb at wavelengths that are also “blue-shifted” relative totheir linear or branched homologues. These structures serve toblue-shift the edge of absorbance to shorter wavelengths, and thus, toreduce the optical dispersion of UV-cured resins in the visible range ofthe spectrum.

In embodiments of the present invention, these results are achieved intwo ways. First, by the incorporation of at least about 50% ofcycloaliphatic group-containing monomers into the resins. Second, by thereaction of at least two additives selected from the group consisting ofa hydroxyoxetane, a glycidyl ether, divinyl ether, and alcohols, and inone particular embodiment, both a hydroxyoxetane and a diglycidyl ether,with resins to form a crosslinked (or cured—used interchangeably) solidhybrid polymer.

The use of about 50% or more of cyclic aliphatic group-containingmonomers in the PT curable resin, and/or the use ofcycloaliphatic-containing additives, to raise the total cycloaliphaticcontent of the cured solid hybrid polymer, not only results in goodphysical properties, but also very desirable optical properties. Theaddition of selected additives, and in one embodiment a hydroxyethyloxetane reagent and a glycidyl ether, such as glycidyl-cappedpoly-dimethylsiloxane (Gelest DMS-E09), to the PT curable resin,followed by curing to form a solid hybrid polymer, provides thenecessary additional fracture toughness/high cohesive strength missingfrom, e.g., optically known ECHETMS-based polysiloxane polymers, withoutimpacting the excellent optical properties of the PT curable resin to adegree which prevents them from being used. Optical devices producedfrom this material and coatings produced for use on optical devices madefrom this material are also contemplated.

As used herein, “cycloaliphatic group” means a cyclic group that is notaromatic. Cycloaliphatic groups include monocylic and polycylic groups.Typically, the cycloaliphatic group contains from 3 to 15 carbon atoms,in embodiments from 4 to 12 carbon atoms, and in another embodiment from5 to 10 carbon atoms. In one embodiment of the present invention thecycloaliphatic group is a polycyclic group.

The basic ring structure of the cycloaliphatic group is not restrictedto groups formed solely from carbon and hydrogen (hydrocarbon groups),although a hydrocarbon group is preferred. Furthermore, the hydrocarbongroup may be either saturated or unsaturated, but is preferablysaturated.

In embodiments of the present invention, the basic ring structure of thecycloaliphatic group may include a hetero atom, such as O, S, or F. Inone embodiment, the basic ring structure of the cycloaliphatic groupincludes an oxygen atom in ether form (i.e., R—O—R).

Examples of cycloaliphatic groups include monocycloalkanes, such ascyclopentyl and cyclohexyl, and polycycloalkanes, such as adamantyl,norbornyl, di-norbornyl, isobornyl, tricyclodecanyl,tetracyclododecanyl, or diamondoid derivatives.

Name Structure Cyclopentyl

Cyclohexyl

Adamantyl

Norbornyl

Di-norboryl

Isobornyl

Tricyclodecanyl

Exemplary cycloaliphatic groups (the side alkyl groups shown in thestructures above represent possible attachment points).

The cycloaliphatic groups may be incorporated into the backbone of theresin or may be found as a side-chain on the monomer(s) polymerized toform the resin, or both. In addition, as described below, additives tothe resins may contain cycloaliphatic groups, as well.

The photocurable and/or thermally curable resins (“PT curable resins”)useful in the present invention are any photocurable and/or thermallycurable resin achieving the optical and/or physical properties taughtherein. Examples of suitable PT curable resins include (meth)acrylateresins and polysiloxane resins.

In an embodiment of the present invention, the PT curable resin is a PTcurable (meth)acrylate resin. Briefly, (meth)acrylates contain a vinylmoiety that may be polymerized through free-radical polymerization toform crosslinked polymers. For example, the polymerization of methylmethacrylate to form poly(methyl methacrylate) is shown below:

(Meth)acrylate monomers may contain more than one (meth)acrylatefunctional group. Polymerization of such monomers would producecross-linked resins.

Moreover, the (meth)acrylate monomers may comprise cycloaliphaticgroups. Thus, the resin produced would comprise cycloaliphatic groups asside chains or as part of the backbone of the resin. Examples ofsuitable (meth)acrylate monomers include:

Monomer Structure Name

Adamantylacrylate

Adamantylmethacrylate

Tricyclo [5.2.1.0] decane dimethanol diacrylate

Tricyclo [5.2.1.0] decane dimethanol dimethacrylate

Exemplary cycloaliphatic(meth)acrylate monomers.

In one embodiment of the present invention, the PT curable resin is a PTcurable polysiloxane resin. In one aspect of the invention the PTcurable polysiloxane resin useful in the fabrication of the opticaldevices, such as optical devices and coatings, comprises the reactionproducts of siloxane monomers as shown in Formulae I-III:

wherein x, y and z are mole % or another indication of the relativeproportion of these monomers in the resulting PT curable polysiloxaneresin and where there must be at least some amount of one of Formula Ior Formula III, there must be at least some amount of Formula II, and atleast some of the monomers of Formula II include cycloaliphatic groups,in the resulting polysiloxane resin. Indeed, raising the cycloaliphaticcontent of the PT curable polysiloxane resin, without increasing theepoxy content (or content of other PT curable groups), is believed to beimportant to the optical properties of the PT curable polysiloxane resinconsidered herein as useful in producing optical devices with desirableproperties. At least about 50% of all siloxane monomers used in the PTcurable polysiloxane resins of the invention should include acycloaliphatic group. It will be appreciated that if certaincycloaliphatic group-containing additives are used to produce curedsolid hybrid polymers in accordance with the invention, thecycloaliphatic-containing siloxane content of the PT curablepolysiloxane can be less than 50% as long as the total cycloaliphaticcontent of the hybrid polymer is at least about 15% by weight, or inanother embodiment, at least about 20% by weight, or in still anotherembodiment, about 40% by weight or more. In still another embodiment,the amount of cycloaliphatic groups range from about 18 to about 50% byweight of the hybrid. At least 10% of the silane monomers include acycloaliphatic group substituted with an epoxy group or other PT curablegroup. In another embodiment, the content of photo/thermal crosslinkinggroups (PT curable groups) is at least 20% molar or equivalent contentrelative to the siloxane content of the resin.

Referring back to the reaction products of siloxane monomers, R₁ is analkoxy group of 1 to 2 carbons in length (methoxy or ethoxy), R₂ is acyclic aliphatic group of 3 to 8 carbons in length, one or more of whichcarbon atoms may be replaced with a hetero atom selected from the groupconsisting of O, S, or F, the cyclic aliphatic group being bound to theSi atom through an alkyl bridge of 1 to 6 carbons and being substitutedwith at least one thermally or photo crosslinkable group (PT curablegroup) capable of crosslinking upon application of sufficient heatand/or light (either at the UV or other portions of the spectrum) in thepresences of an effective amount of a suitable initiator. These PTcurable groups include epoxies, vinyl ethers, oxetanes, glycidylethers,acrylates or methacrylates, wherein more than one type of PT curablegroup may be present in the PT curable polysiloxane resins of theinvention; R₃ and R₄ may be the same or different, and are selected fromthe group consisting of: (1) an alkyl group of 1 to 6 carbons, the alkylgroup being straight or branched, substituted or unsubstituted; (2) acyclic aliphatic group of 3 to 8 carbons in length, one or more of whichcarbon atoms can be replaced with a hetero atom selected from the groupconsisting of O, S, or F, the cyclic aliphatic group being bound to theSi atom directly or through an alkyl bridge of 1 to 6 carbons; (3) analkoxy group of 1 to 2 carbons with the proviso that only one of R₃ andR₄ is an alkoxy group; and (4) R₃ and R₄ can together form a cyclicaliphatic group comprising the Si and 3 to 5 carbons, one of which maybe replaced with a heteroatom selected from the group consisting of O orS; and R₅ is an alkyl group of 1 to 6 carbons which can be linear orbranched.

Optical devices or coatings for optical devices made from these PTcurable polysiloxanes are also contemplated.

In one further embodiment, the PT curable polysiloxane resin comprisesonly siloxane monomers of Formulae I and II (meaning none of FormulaIII). In another embodiment, the PT curable polysiloxane resin comprisesonly siloxane monomers of Formulae II and III (meaning none of FormulaI). In still another embodiment, the PT curable polysiloxane resincomprises siloxane monomers of Formulae I, II and II. In yet anotherembodiment, the PT curable polysiloxane resin comprises a plurality ofdifferent siloxane monomers of one or more of Formulae I, II and III(e.g. one monomer having the structure of Formula I, two differentmonomers having the structure of Formula II and one monomer having thestructure of Formula III). Optical devices or coatings for opticaldevices made from these PT curable polysiloxane resins are alsocontemplated.

At least some of the PT curable polysiloxane resins described herein canbe reacted with up to about 40% of a mixture of at least two of thefollowing additives; a hydroxyoxetane, a glycidyl ether, a divinyl etherand/or an alcohol to form a cured solid hybrid polymer having arefractive index of 1.48 or more, an Abbe number of 45 or more, andsufficient fracture toughness. Optical devices and coatings for opticaldevices made from these materials are also contemplated. It will beappreciated that there are two stages in the formulation of thepolysiloxane resins and hybrids of the invention. The first stage iscondensation of the alkoxy groups (sol-gel or condensation) where thealkoxy groups of R₁ react to form siloxane links. The result of thisstage is a viscous transparent resin consisting of functional siloxaneoligomers and/or polymers. While this can be thought of as acrosslinking reaction, it is not a reaction involving the PT curablegroups. The second stage is the UV photocuring or thermal curing of theepoxy or other PT curable groups. The second stage results in a solidtransparent material (i.e. the optical devices). This “resin” is the“functional” (epoxy-functionalized, for example) siloxane polymer. Inone embodiment, this second crosslinking step of the functional groupsof the polysiloxane resins occurs in the presence of the additives, suchas hydroxyoxetane and glycidyl ethers, to form the solid hybrid polymersof the invention.

Looking at Formula I, II and III above, it will also be appreciated thatthey are provided for illustrative purposes to describe the groups whichcan be the building blocks of the PT curable polysiloxanes of thepresent invention. These Formulae are not meant to represent the exactstructure or order of the resulting siloxane polymer but rather todescribe the content and relative proportions of the monomers therein.Moreover, the actual monomers used would not have exposed oxygens butwould be capped with, for example alkyl groups to form alkoxy groupswhich are removed during the polymerization process.

The PT curable polysiloxanes of the invention may be random copolymers,block copolymers, random-block copolymers and the like. The final orderand structure of the PT curable polysiloxane will depend on a number offactors, including the reaction conditions, the relative reactionkinetics of the individual monomers, the relative prevalence orabundance of each monomer, the order of their addition, the number andtype of reactive groups on each monitor, and the like.

By way of illustration, consider the following non-limiting examples ofshort segments of hypothetical PT curable polysiloxanes where:dimethylsiloxane is represented by the letter M,cyclohexylmethyldimethoxysilane is represented by the letter C,trimethoxypropylcyclohexylepoxysilane is represented by the letter T,and dimethoxymethylpropylcyclohexylepoxysilane is represented by theletter D (it will be appreciated that these refer to the actualmonomers, methyl groups from the methoxy groups which form the siloxanebackbone are dislodged). Consider a siloxane polymer comprised of threemoles of T, two moles of D, and five moles of C. Exemplary structurescould be represented by: TCDCTCDCTC, TTCDDCCTCC, and TTTDDCCCCC. Inanother embodiment, consider a PT curable polysiloxane of three moles ofM, two moles of C, and five moles of T. Exemplary structures could berepresented by: TMTCTMTCTM, TTCMTMMTCT, and TTTTTMMMCC. Finally, asiloxane polymer could be composed of three moles of T, three moles ofD, two moles of M, and two moles of C. Exemplary structures could berepresented by TTTCCMMDDD, TTTMMDDDCC, DTMCDTMCDT, and DDTMDCCTMT.Depending upon the length of the polymer, the relative portions of themonomers used, the order of their additions and the like, almost anyorder or repeat is possible throughout the structure. It is noted,however, that the PT curable polysiloxanes of the invention need atleast about 10%, and often about 20% or more, of its siloxane monomersnecessarily include a PT curable group such as an epoxy substitutedcycloaliphatic group and, in some embodiments, at least about 50% of thesiloxane monomers should include a cycloaliphatic group (with or withoutthe PT curable group).

Other hypothetical illustrative segments of a PT curable polysiloxane inaccordance with the present invention include those of Formulae IV-IX:

In the segments of Formulae IV-VII, the cycloaliphatic epoxy to the leftis of Formula I, the cycloaliphatic epoxy to the right is of FormulaIII, and two or three groups between them are each of Formula II.Formulae VIII and IX comprise Formulae II and III.

Additional trifunctional cyclic groups of Formula II (wherein one of R₃or R₄ is an alkoxy group) that may be used in accordance with thepresent invention include 2-(Bicycloheptyl)trimethoxysilane,Adamantylethyltrymethoxysilane, Cyclooctyltrimethoxysilane,Cyclopentyltrimethoxysilane (Gelest SIC2557.0), and(Cyclohexylmethyl)trimethoxysilane. Difunctional groups of Formula IIthat may be used in accordance with the present invention includedidyclohexyldimethoxysilane, cyclohexylmethyldimethoxysilane (GelestSIC2469.0), and(methoxydimethylsilyl)-6-[2-(methoxydimethylsilyl)ethyl]bicycloheptane.

In all of the above illustrations, R₃ and R₄ of the monomers of FormulaII were separate groups on the siloxane monomers. However, R₃ and R₄ mayform a cyclic group that encompasses the silicon in the backbone. Suchmonomers of Formula II can be used alone or can be substituted for someof the groups of Formula II previously discussed. Consider, forillustration only, the hypothetical PT curable polysiloxane segment ofFormula X:

The monomer to the left is of Formula I, the monomer to the right is ofFormula III, and both central monomers are of Formula II. Other examplesof these aliphatic cyclic monomers of Formula II include:cyclotrimethylenedimethoxysilane, cyclotetramethylenedimethoxysilane,cyclopentamethylenedimethoxysilane, and2,2-dimethoxy-1-Thia-2-silacyclopentane.

Noncycloaliphatic siloxane monomers of Formula II useful includedimethyldimethoxysilane, diethyldimethoxysilane (Gelest SID3404.0),propylmethyldimethoxysilane, diisopropyldimethoxysilane (GelestSID3538.0), and diisobutyldimethoxysilane (Gelest SID3530.0). Anycombination or mixtures of these are contemplated.

In one embodiment, the amount of dimethylsiloxane of Formula II in thepolysiloxane resin is less than about 50% molar fraction relative to thetotal siloxane content.

It will be appreciated that functional monomers that include a freemethoxy or ethoxy group (R₁) would result from the use of any of thetrifunctional cyclic groups and alkoxy-containing aliphatic epoxysilanes, and these groups are crosslinkable with one another, oftenduring the same processing steps which form the PT curable polysiloxane.However, the epoxy groups, depending upon the chemistry, conditions, andreactants used, can remain free for subsequent reaction.

In some embodiments of the present invention, the PT curablepolysiloxane comprises one or more methoxy silane or ethoxy silanegroups. (See e.g., Formulas IV-VIII and X above). These groups appear tocontribute to the adhesion of the resins to glass silica, and metaloxide substrates in general. Accordingly, such methoxy silane and ethoxysilane-containing PT curable polysiloxane resins are useful inapplications where adherence to a glass or metal oxide substrate (Al₂O₃,TiO₂, CrO, etc.) is desired.

The foregoing discussions separately focused on PT curable(meth)acrylate and polysiloxane resins. However, these photocurable orthermal curable groups may be used together. These photocurable orthermal curable groups may also include other photocurable or thermalcurable groups, such as, glycidyl ethers, oxetanes, and vinyl ethers.For example, at least 10%, and in another embodiment, at least about20%, molar or equivalent content of these PT curable groups relative tothe siloxane moiety or acrylate moiety may be present. Acrylates andmethacrylates react by a different mechanism (free radicalpolymerization) than epoxies, oxetanes and vinyl ethers (cationicpolymerization), but both types of polymerizations are not exclusive ofeach other and have been shown in the literature to work together. Forexample, acrylate and methacrylate polymerizations are inhibited byoxygen and the resins may shrink considerably during cure (>3%).However, poly(meth)acrylate resins are known to have excellent fracturetoughness. For these reasons, in some embodiments of the presentinvention, the relative concentration of (meth)acrylates is less thanabout 10% of the equivalent SiO concentration.

Polymerization/curing of the PT curable resins requires the presence ofa photoinitiator(s) or a thermally activated initiator(s). Theseinitiators are widely known. Typical concentrations of these initiatorsare between 0.5% to about 2.5% by weight. Cationic polymerizationinitiators are aryl-iodonium and aryl-sulfonium salts. See Crivello etal. Chemistry of Materials (2001) vol. 13, p. 1932. Free radicalpolymerization initiators are more diverse (Acetophenone family, benzyland benzoil compounds family).

The PT curable resins, once cured, have much, if not all, of thedesirable optical properties of the invention. This can be assessed bycasting a film of this resin and measuring its optical properties byknown techniques. In making optical devices, these PT curable resins maybe used alone or in combination with conventional additives and cured toform a solid polymer.

One way of manufacturing optical devices in accordance with theinvention is replication. Replication involves dispensing a PT curableresin, creating a confined space around the resin to shape the volumeoccupied by the resin, and introducing an induction agent that transformthe resin into a solid optical device that retains the volume/shape. Theinduction or transforming agent can be light, heat, or a combination oflight and heat. Furthermore, the optical device is shaped by confiningthe resin between a flat surface (the substrate) and another surface(the mold) that can also be flat (to make a film or sheet) or could havecomplex geometries, such as concave hemispheres, cylinders, rectangulartroughs, etc. Typical dimensions of these shapes are between 10 nm (e.g.nanoimprint lithography) on the side to about 100 mm on the side, andfrom 10 nm in height, to about 5 mm in height. In consumer opticsapplications, in particular, the devices are between 100 microns on theside to about 10 mm on the side, and their heights are between 10microns and 2 mm. The devices can be replicated one at a time, or inparallel. In the latter case, one could replicate an array of devicessimultaneously on a single substrate (wafer). The wafer can be as smallas 25mm (1″) or as large as 300 mm in diameter. Since each deviceoccupies a small area of the wafer, tens to thousands of devices can bemanufactured simultaneously on a given wafer. After replication, thestamper tool is removed, and the wafer can be processed to add moredevices, on the back side for example, or it can be diced to isolateeach individual device. Dicing could be a source of device edgedelamination or film fracture (seehttp://polymers.nist.gov/combi/NCMC-8%20CD/01_Presentations/Update_(—)4_Kim.pdf.)

Resin materials of both desirable physical and optical properties of thepresent invention can be formed by blending and reacting thecrosslinkable, PT curable resins of the invention with at least twoadditives selected from the group consisting of a hydroxyoxetane, aglycidyl ether, a divinyl ether and an alcohol. It is known that theaddition of these additives individually can provide improved physicalproperties to certain resins.

For example, when a combination of some of these materials were added toa polysiloxane composed of 70 mole % trimethoxypropylcyclohexyl epoxysilane and 30 mole % of dimethylsiloxane, as well as a polysiloxane of33 mole % trimethoxypropylcyclohexyl epoxy silane, 33 mole %dimethoxymethylpropylcyclohexyl epoxy silane, and 33 mole % ofdimethylsiloxane, they showed significant improvement in terms of theirphysical properties. In particular, an array of 161 concave lenses each1.7 mm in diameter and ˜150 microns in depth were fabricated on 2″ glasswafer by photocuring replication of the resin using an elastomeric mold(PDMS). The wafer was subjected to 30 minutes of annealing at 130° andthen returned to room temperature without evidence of delamination orcracking. However, as these crosslinkable siloxanes were not PT curablepolysiloxane resins in accordance with the present invention, they didnot have the desired level of all of the optical properties previouslydiscussed. The use of a PT curable polysiloxane resin of the inventionis expected to provide both the preferred optical properties, and thedesirable physical properties realized above. Moreover, there was noreason to expect that the combination of these two materials would provesuperior to the use of equal amounts of either.

Fracture toughness is the critical stress intensity K_(c) at which amaterial cracks. Stress intensity K is defined as K=σ√{square root over(c)} where σ is the stress and c is the crack length. The strength ofthe material a σ_(break) is related to fracture toughness byσ_(break)=K_(c)/√{square root over ((πc))}. Materials with K_(c)<3 MPam^(1/2) are generally considered brittle (ice K_(c)˜0.1 MPa m^(1/2),Epoxies K_(c)˜1-3 MPa m^(1/2), polystyrene K_(c)˜2 MPa m^(1/2)).Thermoplastics (Nylon, HDPE) are generally tougher (K_(c)˜4 MPam^(1/2)), and engineering composites are considered “tough” byengineering standards (K_(c)>20 MPa m^(1/2))(see enclosed reference M.F. Ashby, Materials selection in Mechanical Design, Pergamon Press,Oxford 1992.)

As an approximation, fracture toughness scales with strength. Estimatedtoughness by measuring tensile strengths on dogbones-shaped samples, andintegrating the area under the stress-strain curves to account forelongation to failure may be used. Room-temperature values of toughnessabove 1.49 MPa result in robust optical devices, but below 0.5 MPatypically resulted in material cracking upon thermal cycling.

Since the issue of fracture toughness (4) substrate adhesion (8), andstamper release are closely associated to manufacturability andreliability (reflowability and thermal shock), a better way to quantifythese parameters would be to define a set of conditions that the devicesmust pass without cracking (4) or separating from their substrates (8).These are: A replication process that involves hardening the UV-curableresin between a rigid (glass wafer) substrate and a more flexiblereleasable mold (stamper), followed by a thermal annealing process(example 30 minutes at 10° C., and more typically 1.49 h. at 130° C.).The stamper wafer (typically 6″ diameter or larger) should release fromthe cured resin (before or after annealing) without causing either thestamper or the cured resin to delaminate or tear from theircorresponding wafers (this is requirement 7). In addition, the curedresin should adhere sufficiently well to the substrate to withstandwafer dicing. Finally, both the adhesion to the substrate and fracturetoughness of the cured resin should be strong enough to withstandthermal shock and humidity testing, as described by internationalstandards IEC60068-2-14 (1984), IEC60068-2-1 (2007), and IEC60068-2-2(1974) from the International Electrotechnical Commission, herebyincorporated by reference, without cracking or separating. Accordingly,another way to describe an optical device having sufficient fracturetoughness is if it is capable of withstanding replication, wafer dicingand reliability testing and this is what is meant by high fracturetoughness.

The amount of the specific additives used to produce the cured solidhybrid polymers of the invention, such as a mixture of a hydroxyoxetaneand glycidyl ethers, should not total more than about 40% by weight ofthe final cured solid hybrid polymer and, in another embodiment, about1-30% by weight. In still another embodiment, the amount ranges fromabout 1 to about 20% by weight. The relative proportion of each of thesetwo crosslinkable additives can range from 90:10 to 10:90. In otherembodiments, the ratio is about 2:1 to about 1:2, and in still anotherembodiment, about 1:1.

The selection of the materials for copolymerization with the resins ofthe invention are important to the resulting properties. A non-hydroxysubstituted oxetane would be less successful (although its use incombination with a separate alcohol is contemplated and might besuccessful). Amine substituted oxetanes are not compatible with cationicphotoinitiation.

Hydroxyoxetanes useful in accordance with the invention include, withoutlimitation, 3-hydroxymethyloxetans of the structure

where R₆ can be a linear, branched or cyclic alkyl group or a siloxane.Instead of a hydroxymethyl group, other short chain hydroxy alkyl groupof up to 6 carbons may be used and these may be polyols as well. In oneparticular embodiment, R₆ includes cycloaliphatic group(s), which mayalone or with other additives, increase the overall cycloaliphaticcontent of the resulting crosslinked solid hybrid polymer to at leastabout 15% by weight, in another embodiment, at least about 20% byweight, and in another embodiment, about 40% by weight or more.

Glycidyl ethers that may be used in accordance with the presentinvention may include, without limitation, diglycidyl ethers of thefollowing formula:

where R₇ can be or include a linear alkyl, branched alkyl, or cycloalkylgroup, poly-ethylene glycol, mono alcohol or polyol, or a siloxane.Again, in one particular embodiment, R₇ is or includes one or morecycloaliphatic group to increase the overall cycloaliphatic content ofthe resulting crosslinked solid hybrid resin. Indeed, in one embodiment,the content of the cycloaliphatic group found in the PT curablepolysiloxane resin of the invention may be reduced to less than 50% ifR₆ and/or R₇, alone or with other additives, include sufficientcycloaliphatic groups such that the cycloaliphatic content of the hybridpolymer is at least about 15% by weight, in another embodiment, at leastabout 20% by weight, and in another embodiment, about 40% by weight ormore.

Examples of digycicyl ethers useful in accordance with the inventionare:

Divinyl ethers of the formula:

where R₈ can be a linear, branched or cycloaliphatic alkyl groups, orsiloxanes may also be used as one of the two additives. Examples ofdivinyl ethers:

Again, R₈ may include cycloaliphatic groups which can reduce the amountof such groups necessary in the PT curable polysiloxane as describedherein.

Alcohols that may be used as one of the two additives may include thosewith the general formula

where R₉ and R₁₀ can be H, alkyl, branched alkyl, or cycloalkyl groups,poly-ethylene glycol or siloxanes. R₉ and R₁₀ can also containadditional alcohol functional groups, to form dialcohols, or polyols,including polyvinyl alcohol.

Preferred alcohols are dialcohols and polyols. An example of a suitablepolyol useful as an additive in the present invention includetricyclodecane dimethanol (TCDA-OH)

and derivatives thereof. These polycyclic polyols have the additionaladvantage of also containing a cycloaliphatic group. An example of aTCDA-OH derivative useful in the present invention is the product of thereaction of TCDA-OH and a glycidyl ether epoxy:

The resulting polycyclic polyol compound is both a polyol and containsmultiple cycloaliphatic groups. Use of this additive produces a PTcurable resin that is both tough and has a high T_(g).

EXAMPLE 1

The optical properties, i.e. refractive index and Abbe number(dispersion), of linear and branched (meth)acrylate resins were comparedto the optical properties of cycloaliphatic(meth)acrylate resins. Thetable below summarizes the results:

Refractive Abbe Index (at Number Monomer Structure Name 589 nm) (Vd)

Trimethyolpropane triacrylate (“TMPTAc”) 1.5115 50.2

Trimethyolpropane trimethacrylate (“TMPTMA”) 1.5121 49.5

1,4-Butanediol diacrylate (“BDDA”) 1.5075 52.6

1,4-Butanediol dimethacrylate (“BDDMA”) 1.5117 51.0

Adamantylmethacrylate 1.5289 53.1 ± 1.0 

Tricyclo [5.2.1.0] decane dimethanol diacrylate (“TCDDDA”) 1.5308 53.4 ±0.3 

In sum, the cycloaliphatic(meth)acrylate resins had both a higherrefractive index and a higher Abbe number as compared to the linear andbranched (meth)acrylate resins. The cycloaliphatic(meth)acrylate resinshad a refractive index greater than 1.525 and an Abbe number greaterthan 53.

EXAMPLE 2

The optical properties, i.e. refractive index and Abbe number(dispersion), and T_(g) of numerous PT curable resins were evaluated asfollows. The (meth)acrylate reagents and TATATO were purchased fromAldrich Chemical and used as-received. The thiol reagent (4T) waspurchased from Evans Chemetics LP (Waterloo, N.Y.). A typicalformulation involved mixing 2 g to 4 g of the desired monomerformulation with 0.5 w/% of photoinitiator, PI (Irgacure 184, purchasedfrom Aldrich). The monomers and the PI were mixed thoroughly using aFlacktek Speedmixer model DAC 150 FVZ-K. typical mixing protocolinvolved 3 minutes rotation at 2,000 rpm.

The mixed formulation was then poured into a rectangular mold(approximately 3 mm tall, 5 mm wide and 10 mm long). The bottom of themold consisted of an elastomer gasket attached to a glass slide. Afterfilling the mold with the resin, the mold was caped with a glass slideand the assembly was secured with spring-loaded clamps. The bottom andtop surfaces of the mold were transparent to UV light.

Resin curing was achieved with the UV system Asahi Spectra Max 302. Atypical protocol involved 90 seconds exposure through the top windowusing a low intensity setting (usually 1 to 3 mW/cm2), followed byadditional 90 second low intensity exposure through the bottom window(the mold was flipped). The intensity of the beam was then adjusted toabout 10-15 mW/cm2 and the exposure process was repeated, 90 secondseach side. This two-stage curing protocol was adopted in order to avoidthe rapid release of heat and bubble formation.

After the sample was thoroughly UV cured, it was annealed between 130°C.-160° C. on a hot plate for about 30 minutes. Afterwards the curedblock was carefully de-molded, and at least two of its faces were groundand polished. Typically, one of the front faces (3 mm×5 mm) and one ofthe window faces (5mm x 10mm)were ground and polished. This last stepwas necessary for measuring the optical properties.

The Abbe numbers and Refractive Indices were measured using an Atagomultiwavelength refractometer. The resin block was optically coupled tothe flat glass sample holder of the refractometer using a coupling fluidof refractive index higher than that of the block (usuallybromonaphthalene). A halogen light source was used in conjunction withnarrow band filters to illuminate the polished end of the cured block.The Refractive indices were measured at three wavelengths: L1=489 nm,L2=488 nm, and L3=656 nm at least five times each. The Abbe numbers werecomputed from the usual equation Vd=(R1-1)/(R2-R3), where R1, R2 and R3are the refractive indices at L1, L2 and L3 respectively.

Sample bars for determination of the glass transition temperature(T_(g)) and cross-link density were fabricated with a similar moldingtechnique. Glass transitions were determined by a double cantilevertechnique in a dynamic mechanical analyzer Perkin Elmer DMA 8,000.

As used below, “4T” means pentaerythritol tetrakis(3-mercaptopropionatewith a structure of:

“TATATO” means 1,3,5-triallyl-1,3,5-triazine-2,4,6-trione, which has astructure of:

“PMA” means perfluorocyclohexyl methyl acrylate, which has a formula of:

The tables below summarize the results of these evaluations:

Refractive Abbe Compound T_(g) Index Number 4T TATATO (° C.) (at 589 nm)(Vd) 4.16 g 2.82 g 66 1.5638 45.0 0.0085 mol 0.01133 mol Thiol-ene resin(4T-TATATO).

This resin has a high refractive index, but low Abbe number. Thus, thesemonomers can be used in conjunction with (meth)acrylates to increaserefractive index, but will lower the Abbe number.

Refractive Abbe Compound T_(g) Index Number TMPTAc 4T TATATO (° C.) (at589 nm) (Vd) 2.63 g 4.16 g 2.83 g 74 1.5498   47 ± 0.5 0.0089 mol 0.0085mol 0.0114 mol 2.63 g 4.16 g 0 1.3 1.5362 48.3 ± 0.5 0.0089 mol 0.0085mol 100% 0 0 >100 1.5115 50.2 Thiol-ene acrylate (4T-TATATO-TMPTAc).

Refractive Abbe Compound T_(g) Index Number TMPTMA 4T TATATO (° C.) (at589 nm) (Vd) 2.57 g 3.57 g 2.43 g 92 1.5483 46.6 0.0076 mol 0.0073 mol0.0097 mol 3.00 g 4.16 g 0 23 1.5360 48.7 0.0089 mol 0.0085 mol 100% 0 0NA 1.5121 49.5 Thiol-ene acrylate (4T-TATATO-TMPTMA).

Refractive Abbe Compound T_(g) Index Number BDDA 4T TATATO (° C.) (at589 nm) (Vd) 2.64 g 4.16 g 2.83 g 47 1 5475 46 9 0.0133 mol 0.0085 mol0.0114 mol 2.64 g 4.16 g 0 −20 1.5296 50.0 0.0133 mol 0.0085 mol 100% 00 75 1.5075 52.6 Thiol-ene acrylate (4T-TATATO-BDDA).

Refractive Abbe Compound T_(g) Index Number BDDMA 4T TATATO (° C.) (at589 nm) (Vd) 3.54 g 4.16 g 2.83 g 58.4 1.5411 49.0 0.0156 mol 0.0085 mol0.0114 mol 3.54 g 4.16 g 0 −5.2 1.529 50.4 0.0156 mol 0.0085 mol 100% 00 NA 1.515 51 Thiol-ene acrylate (4T-TATATO-BDDMA).

Refractive Abbe Compound Index Number 4T TCDDDA (at 589 nm) (Vd) 0.23 g1.17 g 1.53688 52.4 0.00048 mol 0.0038 mol Cycloaliphatic acrylate withthiol (4T-TCDDA).

In sum the presence of heterocycle (TATATO) and/or thiols (4T) increasesrefractive index and lowers the Abbe number of (meth)acrylates.

Refractive Abbe Compound Index Number 4T TCDDDA PMA (at 589 nm) (Vd)0.58 g 2.92 g 1.5 g 1.5034 55.3 0.00119 mol 0.0096 mol 0.0041 molCycloaliphatic acrylate with thiol and fluoroacrylate (4T-TCDDA-PMA).

Thus, with the presence of a thiol and fluoroacrylate produces a highAbbe number (greater than 55), but the refractive index is lowered in acycloaliphatic acrylate.

The data from Examples 1 and 2 (with the exception of T_(g) data) ispresented in FIG. 1.

As shown in FIG. 1, the gap between cycloaliphatic acrylates andnon-cyclic acrylates is about 3 Abbe number units. Thus, the use of thecycloaliphatic acrylates produces a significant decrease in opticaldispersion over the linear and branched acrylates.

EXAMPLE 3

In a laboratory equipped with yellow lighting we added 4.5 g of3-Methyl-3-oxetanemethanol (Prod. No. 277681 from Sigma Aldrich,Milwaukee, Wis.) and 4.5 g of Epoxypropoxypropyl terminatedpolydimethylsiloxane, 8-11 cSt (Prod. No. DMS-E09 from Gelest,Morrisville, Pa.) to a glass vial and mixed the liquids vigorously for 5minutes using vortex mixer (Model K-550-g from VWR). Once mixed, thevial was degassed inside a vacuum desiccator to remove trapped airbubbles. In a separate 50 g capacity disposable container (fromFlackTek, Landrum, S.C.), we weighed 21 g of the resin PCX-35-67B(epoxycyclohexyl siloxane and diaryliodonium hexafluoroantimonate(photoinitiator) from Polyset Company, Mechanicville, N.Y.), 4.5 g of1,4-butanediol diglycidyl ether (from Sigma Aldrich, Milwaukee, Wis.),and added the pre-mixed solution 3-Methyl-3-oxetanemethanol andEpoxypropoxypropyl terminated polydimethylsiloxane. We blended thefour-component system for 5 minutes at 2400 rpm using a speedmixer (fromFlackTek DAC 150 FVZ-K series). The blend, a transparent colorlessviscous resin, was labeled TESS-F17 and was stored in the dark.

A two inch (50 mm) diameter stamper containing an array of 261 features(lenses) was fabricated by replicating a Nickel master using a thermallycured elastomeric resin. Each feature (lens) in the master consists in acircular structure approximately 1.6 mm in diameter and 60 microns indepth. The stamper was fabricated by mixing a two-part elastomeric resinaccording to the manufacturer instructions and degassing the resin undervacuum to remove gas bubbles. Approximately 2 to 3 g of the elastomerresin was poured on a fused silica backplane (approximately 6 inchdiameter, 20 mm thick having spacers around its perimeter, approximately300 microns in height. The Nickel master was carefully placed on top ofuncured elastomer, which spread between the two surfaces until themaster rested on the spacers separating the master from the glasssubstrate, The assembly was baked in an oven until the elastomer wascured. Afterwards, the assembly was allowed to cool to room temperature.The Nickel master was carefully removed, leaving behind a replica of itspattern on the elastomer sheet (ca 300 microns thick) still attached tothe backplane.

A 2″×3″ inch glass 1.2 mm thick glass substrate (Fisher Brand22-267-013) was thoroughly cleaned using Nanostrip solution for 2 hrs,followed by rinsing with deionized water and air dried. Afterwards thesubstrate was treated in ECR O2 plasma for 5 minutes (TePla 660).Between 2 and 3 mL of blend TESS-F17 was carefully dispensed on theglass substrate. The stamper was carefully placed on the glass substratecausing the TESS-F17 resin to flow and fill the region between the glasssubstrate and the backplane. The assembly was placed under theultraviolet beam of a Mercury Lamp (Omnicure 52000 from Exfo Inc) at 17mw/cm2 for a total exposure of 2 J/cm2 (2 minutes). Afterwards thestamper was removed from the glass-supported cured TESS-F17 blend. Thecured TESS-F17 blend resin exhibited a transparent and colorless replicaof the stamper.features (lens array) approximately 300 microns tall. Theglass-supported lens array was annealed on a hot plate (Super Nuovadigital hot plate from Barnstead Thermolyne) at 135° C. for 30 minutes,and brought to room temperature afterwards. The lens array appeared as ahard transparent, colorless patterned film robustly attached to theglass substrate. The cured TESS-F17 blend resin had a refractive indexof 1.496 and an Abbe number of 55.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A method of providing fracture toughness and durability to aphotocurable and/or thermally curable resin comprising curing aphotocurable and/or thermally curable resin with an effective amount ofat least two additives selected from the group consisting ofhydroxyoxetanes, diglycidyl ethers, alcohols and divinyl ethers.
 2. Themethod of claim 1, wherein said at least two additives comprisehydroxyoxetane and a glycidyl ether, wherein said curing produces acrosslinked solid hybrid polymer material.
 3. The method of claim 1,wherein said photocurable and/or thermally curable resin comprisesmonomers selected form the group consisting of (meth)acrylate monomers,polysiloxane monomers, and combinations thereof.
 4. The method of claim3, wherein at least 50% of said monomers include at least onecycloaliphatic group.
 5. A photocurable and/or thermally curable resinhaving a refractive index of greater than 1.48 and optical dispersion,as measured by an Abbe number, of greater than
 45. 6. The photocurableand/or thermally curable resin of claim 5, wherein the refractive indexof said photocurable and/or thermally curable resin is greater than 1.49and the Abbe number is greater than
 53. 7. The photocurable and/orthermally curable resin of claim 5, wherein said photocurable and/orthermally curable resin comprises monomers selected form the groupconsisting of (meth)acrylate monomers, polysiloxane monomers, andcombinations thereof.
 8. The photocurable and/or thermally curable resinof claim 7, wherein at least 50% of said monomers include at least onecycloaliphatic group.
 9. The photocurable and/or thermally curable resinof claim 7, wherein said photocurable and/or thermally curable resincomprises a (meth)acrylate monomer selected from the group consisting ofadamantylacrylate, adamantylmethacrylate, tricyclo[5.2.1.0]decanedimethanol diacrylate, tricyclo[5.2.1.0]decane dimethanoldimethacrylate, and combinations thereof.
 10. The photocurable and/orthermally curable resin of claim 8, wherein said photocurable and/orthermally curable resin comprises at least two additives selected fromthe group consisting of hydroxyoxetanes, diglycidyl ethers, alcohols anddivinyl ethers.
 11. The photocurable and/or thermally curable resin ofclaim 10, wherein said at least two additives comprise hydroxyoxetaneand a glycidyl ether.
 12. A crosslinked solid hybrid polymer materialproduced by curing a mixture of PT curable resin and at least twoadditives selected from the group consisting of hydroxyoxetanes,diglycidyl ethers, alcohols and divinyl ethers.
 13. The crosslinkedsolid hybrid polymer material of claim 12, wherein said at least twoadditives are hydroxyoxetane and a glycidyl ether.
 14. The crosslinkedsolid hybrid polymer material of claim 12, having a refractive index ofgreater than 1.48, an Abbe number of greater than 45, a linear cureshrinkage of less than 3%, and high fracture toughness.
 15. Thecrosslinked solid hybrid polymer material of claim 12, having arefractive index greater than 1.49, an Abbe number greater than 53,linear cure shrinkage of less than 2%, and high fracture toughness.